Aerial drop penetration device

ABSTRACT

Aerial drop penetration devices constructed in accordance with this invention exhibit a reduction of mass at implant by separating into two separate masses (that is, the two mating parts of the device); a small mass penetrates less than a large mass. The small mass (or aft part) contains a transmitting antenna which remains above the soil surface for transmitting a radio frequency signal. Attached to this mass are terra spikes which include detents as part of a release mechanism. The large mass (or forward part), the actual penetration device, contains electronic circuitry responsive to subsurface vibrations. The small mass is coupled to the large mass during the aerial drop by means of retaining pins engaging the detents of the spikes. The release means is actuated when the terra spikes penetrate the soil surface. These spikes also provide the force necessary to decelerate the small mass to a stop.

United States Patent [191 McElwain et al.

[4 1 Jan. 7, 1975 AERIAL DROP PENETRATION DEVICE [73] Assignee: Texas Instruments Incorporated,

Dallas, Tex.

22 Filed: Apr. 9, 1969 21 Appl. No.: 815,524

[52] US. Cl 340/15.5, 102/62,v 102/88, 114/209, 175/19, 325/102, 340/2, 340/17 [51] Int. Cl E021 5/20, G01s1/72, GOlv 1/16 [58] Field of Search 325/102; 340/2, l8, 17; 175/19, 22; 181/.5 EC; 102/62, 88, 92.4; 114/209 [56] References Cited UNITED STATESv PATENTS 948,148 2/1910 Schenk 102/62 2,265,697 12/1941 Neumann et al. 102/62 3,115,831 12/1963 Suter 340/2 3,230,500 1/1966 Dunn 340/2 X 3,281,765 10/1966 Taplin 3,309,649 3/1967 Ballard et al. 3,444,508 5/1969 Granfors et al.... 340/2 3,474,405 10/1969 Padberg, Jr 340/17 X Davis, Jr. et a1 340/l5.5 Kriesel et al 102/62 X Primary Examiner-Malcolm F. llubler Attorney, Agent, or Firm-Harold Levine; Rene E. Grossman; Leo N. Heiting [57] ABSTRACT Aerial drop penetration devices constructed in accordance with this invention exhibit a reduction of mass at implant by separating into two separate masses (that is, the two mating parts of the device); a small mass penetrates less than a large mass. The small mass (or aft part) contains a transmitting antenna which remains above the soil surface for transmitting a radio frequency signal. Attached to this mass are terra spikes which include detents as part of a release mechanism. The large mass (or forward part), the actual penetration device, contains electronic circuitry responsive to subsurface vibrations. The small mass is coupled to the large mass during the aerial drop by means of retaining pins engaging the detents of the spikes. The release means is actuated when the terra spikes penetrate the soil surface. These spikes also provide the force necessary to decelerate the small mass to a stop.

16 Claims, 10 Drawing Figures TEXTWTEU 7 i975 COUPLER SENSOR AMPLIFIER 8 TRANSMITTER POWER SUPPLY SHEET .2 OF 4 FIG. 4

SHEET 3 OF 4 R E T W M S N A R T POWER SUPPLY SENSOR FIG. 3

FIG. IO

PATENTEUJAH H915 3,859.598

SHEET a 0F 4 FIG. 9

AERIAL DROP PENETRATION DEVICE This invention relates to penetration devices, and more particularly, to a separable two-part aerial drop probe for detecting subsurface vibrations.

Heretofore, the depth of penetration of aerial drop probes released from airborne carriers depended upon: the soil condition, velocity at implant, body weight, configuration, and nose shape. Often the complete body of the probe was submerged below the soil surface. Since such devices usually contain electronic and scientific instruments that transit subsurface information relative to the soil to a remote receiver, it is necessary to maintain a transmitting antenna above the soil surface to permit transmission of radio frequency signals containing the information to a receiving station. With probes of the type that completely submerge themselves below the soil surface, the transmitting antenna may also be submerged and thus prevent transmission of information signals. Typical of earlier one piece probes is that described in the U.S. Pat. No. 3,360,772 issued Dec. 26, 1967.

In addition to investigating subsurface soil conditions, aerial drop probes have also been employed in investigating acoustic sounds traveling through water. The single piece probe of the type described in the above-referenced patent is useless when dropped into a body of water. For waterborne applications, it is essential that a two-part probe be employed with the antenna section remaining on the water surface and the probe section sinking to a predetermined depth. Preferably, the probe should be at a depth ofin excess of forty feet to reduce the noise level pickup.

In the past, sonobuoys have been extensively used for detecting underwater acoustic signals using radio telemetry and an airborne receiver. However, sonobuoys are extremely complex instruments and expensive for routine oceanographic work. Inexpensive and expendable aerial drop measuring devices have been developed to replace the sonobuoy. One such device is described in U.S. Pat. No. 3,226,670 issued Dec. 28, 1965. The probe described in this patent includes a transducer section and an antenna section that are maintained as a single unit during an aerial drop by a friction fit between the two sections. Thus, whether or not the two sections separate is left to chance, since a friction fit does not provide a positive means of separation. Further, the only braking action is that provided by an inflatable bag, and this bag does not inflate until after a chemical has reacted with sea water. The probe may descend a considerable depth before any braking action is produced.

An object of the present invention is to provide an aerial drop penetration device having braking action for both soil and water applications. Another object of the present invention is to provide an aerial drop probe having two parts that separate upon contact with a surface. A further object of the present invention is to provide an aerial drop probe for sensing subsurface vibrations and transmitting information related thereto through a ground level antenna. Still another object of the present invention is to provide an aerial drop probe wherein a small mass remains on the soil or water surface and a large mass penetrates to a greater depth.

In accordance with the present invention, a separable two-part aerial drop probe includes a first section (a light mass) having terra spikes conncted thereto and actuated by contact with the soil surface for braking the first section to a stop. A second section (a large mass) engages the first section in a manner such that the two sections may be easily separated. A releasable couplerjoins the two sections as a single unit during the aerial drop; this coupler is actuated to release the sections from each other upon contact of the probe with the soil surface.

In accordance with a specific embodiment of this in vention, a separable two-part aerial probe for detecting subsurface vibrations includes a first cylindrical housing (a light mass) having an antenna attached thereto for transmitting radio frequency signals. A second cylindrical housing (a heavy mass) having a cone-shaped end mates with the first housing. This second housing contains a transducer and electronic circuitry for converting subsurface vibrations into radio frequency signals which are transmitted from the antenna of the first housing by means ofa flexible cable connecting the two housings. Terra spikes attached to the first housing are actuated by contact with a soil surface to brake the first housing to a stop. Retaining pins attached to the second housing form a releasable coupling with detents in the terra spikes.

A more complete understanding of the invention and its advantages will be apparent from the specification and claims and from the accompanying drawings illustrative of the invention. Referring to the drawings:

FIG. 1 is a perspective view of the two-part aerial drop probe of the present invention;

FIG. 2 is a cutaway view of the lower section of a two-part probe containing the sensing and electronic equipment;

FIG. 3 is a block diagram of an electronic system for sensing subsurface vibrations and! transmitting radio frequency signals representative thereof;

FIG. 4 is an enlarged view partially cutaway of the upper section of the two-part probe;

FIG. 5 is a top view of the upper section with the top plate partially cutaway to illustrate the antenna mechanism; v

FIG. 6 is an enlarged view of a releasable coupling mechanism for joining the upper and lower sections into a single unit;

FIG. 7 illustrates the two-part probe of the present invention implanted in a soft soil;

FIG. 8 is a partial view of the upper and lower sections illustrating an alternate embodiment of a releasable coupling mechanism;

FIG. 9 illustrates a modification of the embodiment shown in FIG. 8 for use in investigating vibrations generated in water; and

FIG. 10 is an overall view of a two-part aerial drop probe for investigation of subsurface vibrations in bodies of water.

Referring to the drawings and in particular to FIG. I, there is shown a two-part aerial drop probe of the present invention including an upper cylindrical shaped housing 10 mating with a lower cylindrical shaped housing 12. Terra spikes 14 are bolted to the upper section 10 and terminate in a triangular shaped lower end. Although only three terra spikes are illustrated, the usual configuration is to have four spikes each displaced around the circumference of the upper section. To guide the probe during an aerial drop, an arrangement of four fins 16 is attached at the upper end of the cylindrical housing 10. These fins 16 are mounted to pivot about a bolt 18 and may thus be stored in a position of alignment with the longitudinal axis of the probe. This arrangement allows for the probe to be stored and dropped from a cylindrical container.

As illustrated in FIG. 2, the lower section 12 terminates in a cone-shaped point 20. Compared to the cylindrical housing 10, the lower section is a relatively heavy mass. The point 20 and a power supply 34 comprise a considerable part of this mass. When the probe of the present invention is employed to detect subsurface vibrations, such as may be set up by the passage of vehicles, troops, or small numbers of soldiers over the surrounding terrain, the point 20 contains a transducer in a chamber 22 that converts vibrations into electrical signals.

As shown in FIG. 3, the electrical signals representative of subsurface vibrations from a transducer 24, which maybe in the chamber 22, are amplified in an amplifier 26 and converted into radio frequency signals in a transmitter 28. The transmitter 28 is connected to an antenna 30 by means of a flexible cable 32. As will be described shortly, the antenna 30 and the cable 32 are stored in the upper cylindrical housing 10. A power supply 34 supplies the electrical energy for operating the various components.

Returning to FIG. 2, the power supply 34, which may be a battery, is physically located in the section 12 in a container 36. The amplifier 26 and the transmitter 28 are assembled into the section 12 in a container 38. The various components for converting subsurface vibrations into radio frequency signals may be interconnected by means of a coupler section 40.

Referring to FIG. 4, there is illustrated a portion of the upper section including one of the fins 16 in a folded position. The fin 16 is spring loaded to move into the position illustrated in FIG. 1 by means of a torsion spring 42. Thus, as the probe of this invention leaves a discharge cylinder, all four fins 16 will assume a guiding position as illustrated in FIG. 1.

Internally, the section 10 includes an antenna base spool 44 having an annular ring 46 for limiting the movement thereof by engaging a shoulder 48 of the housing 10. A deployment spring 50 engages the spool 44 and an antenna base plate 52 to exert an upward force on'the spool. A retaining ring 54 holds the base plate 52 in position.

A vertical whip antenna and a multi-element ground plane are included in the upper housing 10. The four element ground plane 56 is stored in the housing 10 as a coil around the spool 44. These elements expand horizontally into a fan shape when the probe is in a transmitting mode. A whip antenna 58 extends vertically when in the transmitting mode. This antenna is stored in a coiled position around a shear rod 60. The shear rod 60 is held in place by means of a machine screw 62 and a retaining ring 64.

A lid 66 encloses the upper end of the antenna cavity and an O-ring 68 seals the interior of the housing 10 from contamination by dust and other airborne particles. With the lid 66 maintained in place by means of a shear pin 70 engaging the shear rod 60, the whip antenna and the ground plane elements are stored within the housing 10 against the upward acting force of the deployment spring 50.

During storage and transportation of the probe, the lid 66 is secured in the position illustrated by means of a nut 72 threaded onto a retaining rod 74. This nut will be removed prior to dropping the probe from an aircraft. Thus, as the probe implants itself, only the shear pin holds the lid 66 in place.

The pin 70 shears upon impact of the probe thereby releasing the lid 66, and the deployment spring 50 forces the spool 44 upward out of the housing 10. As the spool 44 clears the upper end of the housing, the ground plane elements 56 uncoil. Releasing the lid 66 also permits the whip antenna 58 to be erected vertically by means of an antenna erection torsion spring As illustrated in FIG. 5, the torsion spring 76 engages an antenna erection arm 78 rotatably mounted in a -clamp. 80 on a shaft 82. The erection arm 78 supports the antenna 58 by means of machine screws 84. FIG. 5 also better illustrates the stored position of the antenna 58 as it is coiled around the rod 60. Also illustrated is the connection of the ground plane 56 to the spool 44.

Radio frequency signals produced by the transmitter 28 are connected to the antenna 58 by means of the flexible cable 32. Referring again to FIG. 4, an encapsulant 86 provides a means for storing the flexible cable 32 in the housing 10. This encapsulant is held in the housing by means of a plate 88 and a retaining ring 90, below the retaining ring 64. The cable 32 connects to the transmitter 28 by means ofa coax connector 92. As explained previously, the transmitter 28 is assembled into the section 12 in a container 38. A force ring 94 retains the container 38 in position in the housing 12.

I Referring now to FIG. 6, there is illustrated a releasable coupler for retaining the section 12 as a single unit with the section 10. The terra spikes 14 extend below the end of the section 10 over the upper part of the section 12. Each terra spike 14 includes a detent 96 that engages a retaining pin 98 to lock the sections into a single unit.

In operation, the probe drops from an aircraft with the stabilizing fins 16 maintaining a smooth trajectory as the probe falls. A body in motion possesses a certain amount of kinetic energy depending upon its mass and velocity. This kinetic energy may be expressed as /2 MV With a two mass system such as described herein, the total K.E. (total) K.E. (large mass-section 12) K.E. (small mass-section 10). In order to decrease this kinetic energy to zero, such as when a body is at rest, work must be done on the body. The amount of work expended on each of the two bodies of the probe of the present invention is directly related to its mass. Since one of the bodies has a relatively small mass (the section 10), the amount of work required to reduce its velocity to zero is relatively small.

To perform work on a body, a force is required acting over a period of time. If this force acts in the opposite direction of the body motion, the kinetic energy decreases. The magnitude of a force that reduces the kinetic energy of a body to zero is of interest when considering penetrating probes. For an zir drop penetrating probe, the magnitude of the force that develops will be dependent upon the soil condition for a given body configuration and the velocity at impact. Thus, it is desirable in soft soil conditions to minimize the mass for penetrating devices to limit the depth of penetration.

An important feature of this invention is that it allows for the reduction of the mass of a probe at implant by releasing a single mass system into two separate masses (section and section 12); thus allowing the small mass to penetrate less than the large mass.

Referringto FIG. 7, as the probe penetrates the soil surface, the terra spikes 14 provide the force necessary to decelerate the section 10 (small mass) to a rest position; that is, reduce its kintetic energy to zero. By giving the lower end of the terra spike 14 a slight bend outward, as best illustrated in FIG. 6, the force developed has a component in the axial direction of the probe and a component at right angles to the probe axis. This right angle component causes the terra spike to deflect away from the housing 10. Deflection of the terra spike causes the retaining pin 98 to be released from the detent 96 and the lower section 12 is free to move independent of the upper section 10. The lower section 12 continues to penetrate into the soil until the force developed against the point also brings this mass to rest; that is, reduces its kinetic energy to zero. When the kinetic energy of both masses has been reduced to zero, the upper section 10 will be partially buried with the antenna 58 and the ground plane elements 56 (not shown in FIG. 7) extending above the soil surface. The lower mass 12, however, will be completely buried as it penetrates to a depth where the transducer 24 responds to subsurface vibrations.

As illustrated in FIG. 7, the cable 32 separates from the upper section 10 as the lower section 12 penetrates deeper into the soil. Any subsurface vibrations detected by the transducer 24 and converted into radio frequency signals by the transmitter 28 will be received by the antenna 58 through the cable 32.

Penetrating probes of the type described herein may be used in soil conditions ranging from hard pan to very soft soil conditions. Even as the probe penetrates a soft soil, the terra spikes deflect away from the probe housing. Since the horizontal deflection is a function of the penetration depth, the frontal area of the terra brake (that is, the braking effect) increases with penetration. Thus, the terra brake is able to self compensate its braking effect for various soil conditions by varying the exposed frontal area (braking force) as required and the penetration depth changes only slightly.

Referring to FIG. 8, where the same reference numerals are used for like parts found in previous Figures, there is illustrated a modification of the terra spike braking and release assembly. The upper section 10 is maintained as a single unit with the lower section 12 by retaining pins (not shown) extending from a split friction ring 105 into detents in the terra spikes 14. The friction ring 105 slips over the section 12 and holds this section in place by friction resulting from a radially inward directed force produced by the terra spikes 14. A force ring 100 encircles the lower section 12 and includes a plurality of legs 102 extending along the longitudinal axis of the probe toward the terra spikes 14. The legs 102 have pads 102 at the upper end thereof aligned with the tapered section of the terra spikes 14. The force ring 100 and the legs 102 are maintained in the position illustrated by friction between the inner surface of the ring and the outer surface of the section 12.

Except for the addition of the ring 100 and the legs 102, the probe illustrated in FIG. 8 would be similar to that described with reference to FIGS. l-7. Thus, as the probe drops from a delivering aircraft, the stabilizer fins 16 maintain the probe in a smooth trajectory. As the probe implants itself, the soil exerts an upward force on the ring 100 thereby .driving the legs 102 against the terra spikes 14. Since the total area of the ring 100 in contact with the soil will be much greater than that of the terra spikes alone, the retarding force for decelerating the section 10 to zero will be proportionally greater. Again, there will be a force component causing the terra spikes to deflect outward. As explained previously, this deflection allows the retaining pins to be released from detents in the terra spikes. With the retaining pins released, the section 12 is free to continue penetration into the soil.

In addition to providing a greater retarding force, the force ring 100 also provides a more positive release of the two sections. Assume the probe has an angle of impact less than one or more of the terra spikes may not enter the soil. Although the remaining spikes may decelerate the probe velocity to zero before being completely buried, the retaining pins engaging those spikes not in the soil would prevent the lower section 12 from penetrating deeper than the section 10. Thus, the lower section 12 may not be released from the upper section 10 if all the terraspikes 14 do not enter the soil. With the force ring 100, a radial force component will be applied to all the terra spikes thus insuring separation of the section 12 from the section 10 independent of the entry angle. 1

In addition to detecting subsurface vibrations in soil, the two-part probe of the present invention may also be used for detecting underwater acoustic signals from air craft or ships using radio telemetry.

Referring to FIG. 9, there is shown a modification of the probe of FIG. 8 wherein the force ring has been made hollow to provide storage for an inflatable float 106. Legs 102 again extend vertically from the ring 100 to the terra spikes 14. A cylinder of compressed gas 108 connects to the float 106 by means of a pipe 110. Upon impact with the water or as the probe is released from an aircraft, a lever 112 is pulled to release the compressed gas into the float I06 which then inflates to assume the configuration shown dotted. As the probe enters the water, an upward force is developed by means of the float 106 to decelerate the upper section 10 to zero. In addition, this force acting through the terra spikes 14 opens the friction ring 105 thereby permitting the lower section 12 to descend to a preselected depth below the water surface.

Referring to FIG. 10, there is shown still another modification of the two-part probe of the present invention as it appears for detecting underwater acoustic signals. As the upward force produced by the force ring 100 releases the lower section 12, the lower section descends below the water surface to a depth determined by the length ofa steel cable 114. A float 107, mounted in a ring 109 in a manner similar to the float 106 as illustrated in FIG. 9, positioned at the upper part of the section 10, causes the upper section to float partially above the water surface. The float 107 may be inflated upon impact with the water or as the probe is released from an aircraft. Again, the transmitting antenna will be above the water surface with the probe illustrated in FIG. 10, which is an important feature of the present invention.

Operationally, the water probe functions similarly to the land probe as described with reference to FIG. 7. The transducer 24, which may be a hydrophone responsive to acoustic waves traveling through the water, produces electrical signals which are amplified by the 7 amplifier 26 and converted into radio frequency signals by the transmitter 28. These radio frequency signals are connected to the upper section and by means of the electrical cable 32 and transmitted by means of a whip antenna 58 (as illustrated in FIG. 4 not shown in FIG.

While several embodiments of the invention, together with modifications thereof, have been described in detail herein and shown in the accompanying drawings, it will be evident that various further modifications are possible without departing from the scope of the invention.

What is claimed is:

1. A separable two-part aerial drop probe comprismg:

a first section including a plurality of brake members attached to the exterior of the first section, said brake members each having a surface medium engagement portion for engaging the surface medium to bring the brake members into engagement with the surface medium for braking said section to a stop such that said first section remains partially above the surface,

a second section separably mating with said first section, and

releasable coupling means joining said section as a single unit operatively responsive to the brake action to release said sections from each other upon engagement of said brake members with said surface medium thereby permitting said second section to be buried below the surface.

2. A separable two-part aerial drop probe as set forth in claim 1 wherein said releasable coupling means includes retaining pins as part of the second section engaging detents in the brake members attached to the exterior of said first section forjoining the two sections.

3. A separable two-part aerial drop probe as set forth in claim 2 wherein said releasable coupling means further includes a force ring slidably mounted on the exterior surface of the second section for engaging the brake members of said first section to disengage the retaining pins from the detents upon contact of said force ring with a surface area.

4. A separable two-part aerial drop probe comprismg:

a first section including means for guiding said probe during an aerial drop thereof to a desired surface medium;

a plurality of brake members attached to the exterior of the first section, said brake members each having a surface medium engagement portion for engaging the surface medium to bring the brake members into engagement with the surface medium for braking said first section to a stop such that the first section remains partially above the surface;

a second section separably mating with said first section; and

releasable means joining said sections as a single unit operatively responive to the brake action to release said sections from each other upon engagement of said brake members with said surface medium thereby permitting said second section to be buried below the surface.

5. A separable two-part aerial drop probe comprising:

a first section,

braking means, said braking means including a plurality of terra spikes attached to said first section and bendable to provide braking action such that the first section remains partially above the surface,

a second section separably mating ,with said first section, and

releasable coupling means joining said section as a single unit, said releasable coupling means adapted to release said section from each other upon contact of said brake means with a surface thereby permitting said second to be buried below the surface.

6. A separable two-part aerial drop pro be set forth in claim 5 wherein said releasable coupling means includes retaining pins around the second section engaging detents formed in the terra spikes attached to the first section.

7. A separable two-part aerial drop probe as set forth in claim 6 wherein the releasable coupling means further includes a force ring slidably attached to the second section and engaging the terra spikes attached to the first section to disengage the retaining pins from the detents and cause the initial deflection of said spikes upon contact of said force ring with a surface area.

8. A separable two-part aerial drop probe as set forth in claim 7 wherein said releasable coupling means also includes an inflatable float as part of said force ring to provide a force to disengage the retaining pins from the terra spike detents when the probe falls in a body of water.

9. A separable two-part probe for detecting subsurface vibrations comprising:

a first section including an antenna for transmitting radio frequency signals;

a plurality of brake members attached to the exterior of the first section, said brake members each having a surface medium engagement portion for engaging the surface medium to bring the brake members into engagement with the surface medium for braking said first section to a stop such that said first section remains partially above said surface;

a transducer section separably mating with said antenna section and including means for converting subsurface vibrations into radio frequency signals,

means for electrically connecting the converting means of the transducer section to the antenna of said first section to transmit radio frequency signals representative of the subsurface vibrations; and

releasable coupling means joining said first section to said transducer section to form a single unit operatively responsive to the brake action to release said sections upon engagement of said brake members with said surface medium thereby permitting said transducer section to be buried below the surface.

10. A separable two-part probe for detecting subsurface vibrations as set forth in claim 9 wherein each of said brake members include terra spikes and said releasable coupling means includes retaining pins as part of the transducer section engaging detents formed in the terra spikes of the brake members attached to said first section.

11. A separable two-part probe for detecting subsurface vibrations as set forth in claim 10 wherein said releasable coupling means further includes a force ring slidably mounted on the exterior surface of the trans ducer section and engaging the terra spikes to disengage the retaining pins from the detents upon contact of said force ring with a surface area.

12. A separable two-part probe for detecting subsurface vibrations as set forth in claim 11 including an inflatable float attached to said force ring to force said force ring into engagement with the terra spikes to separate said section and to float said first section partially above the surface when dropped in a body of water.

13. A separable two-part aerial drop probe for detecting subsurface vibrations comprising:

a first cylindrical housing having stabilizing fins for stabilizing the glide path of said probe and including an antenna for transmitting radio frequency signals,

a plurality of terra spikes attached to said first cylindrical housing and bendable into a braking position upon contact with a surface area to brake said housing to a stop such that it remains partially above the surface area,

a second cylindrical housing having a cone-shaped end and separably mating with said first cylindrical housing and including means for converting subsurface vibrations into radio frequency signals,

means for electrically connecting the converting means of the second housing to the antenna of the first housing to transmit radio frequency signals representative of the subsurface vibrations, and

releasable coupling means joining said first housing to said second housing to form a single unit aerial drop probe, said coupling actuated to release said sections upon contact of braking means with a surface area.

14. A separable two-part aerial drop probe for detecting subsurface vibrations as set forth in claim 13 wherein said releasable coupling includes:

retaining pins located around the outer surface of said second housing engaging detents formed in the terra spikes attached to the first housing, and

a force ring slidably encircling the second housing and engaging the terra spikes to disengage the retaining pins from the detents upon contact of said ring with a surface area. l

15. A separable two-part probe for detecting subsurface vibrations comprising:

a first section including an antenna for transmitting radio frequency signals,

a brake means, said brake means including a plurality of terra spikes attached to said first section, a transducer section separably mating with said antenna section and including means for converting subsurface vibrations into radio frequency signals,

means for electrically connecting the converting means of the transducer section to the antenna of said first section to transmit radio frequency signals representative of the subsurface vibrations, and

releasable coupling means joining said first section to said transducer section to form a single unit, said coupling means adapted to release said section upon contact of said brake means with a surface area.

16. A separable two-part probe for detecting subsurface vibrations as set forth in claim 15 wherein said releasable coupling means includes:

retaining pins as part of a friction ring encircling the transducer section engaging detents formed in said terra spikes attached to the first section,

a force ring slidably attached to the transducer section and engaging the terra spikes to disengage the retaining pins from the detents, and

an inflatable float storable in said force ring for producing a force to activate said force ring when in 

1. A separable two-part aerial drop probe comprising: a first section including a plurality of brake members attached to the exterior of the first section, said brake members each having a surface medium engagement portion for engaging the surface medium to bring the brake members into engagement with the surface medium for braking said section to a stop such that said first section remains partially above the surface, a second section separably mating with said first section, and releasable coupling means joining said section as a single unit operatively responsive to the brake action to Release said sections from each other upon engagement of said brake members with said surface medium thereby permitting said second section to be buried below the surface.
 2. A separable two-part aerial drop probe as set forth in claim 1 wherein said releasable coupling means includes retaining pins as part of the second section engaging detents in the brake members attached to the exterior of said first section for joining the two sections.
 3. A separable two-part aerial drop probe as set forth in claim 2 wherein said releasable coupling means further includes a force ring slidably mounted on the exterior surface of the second section for engaging the brake members of said first section to disengage the retaining pins from the detents upon contact of said force ring with a surface area.
 4. A separable two-part aerial drop probe comprising: a first section including means for guiding said probe during an aerial drop thereof to a desired surface medium; a plurality of brake members attached to the exterior of the first section, said brake members each having a surface medium engagement portion for engaging the surface medium to bring the brake members into engagement with the surface medium for braking said first section to a stop such that the first section remains partially above the surface; a second section separably mating with said first section; and releasable means joining said sections as a single unit operatively responive to the brake action to release said sections from each other upon engagement of said brake members with said surface medium thereby permitting said second section to be buried below the surface.
 5. A separable two-part aerial drop probe comprising: a first section, braking means, said braking means including a plurality of terra spikes attached to said first section and bendable to provide braking action such that the first section remains partially above the surface, a second section separably mating with said first section, and releasable coupling means joining said section as a single unit, said releasable coupling means adapted to release said section from each other upon contact of said brake means with a surface thereby permitting said second to be buried below the surface.
 6. A separable two-part aerial drop probe as set forth in claim 5 wherein said releasable coupling means includes retaining pins around the second section engaging detents formed in the terra spikes attached to the first section.
 7. A separable two-part aerial drop probe as set forth in claim 6 wherein the releasable coupling means further includes a force ring slidably attached to the second section and engaging the terra spikes attached to the first section to disengage the retaining pins from the detents and cause the initial deflection of said spikes upon contact of said force ring with a surface area.
 8. A separable two-part aerial drop probe as set forth in claim 7 wherein said releasable coupling means also includes an inflatable float as part of said force ring to provide a force to disengage the retaining pins from the terra spike detents when the probe falls in a body of water.
 9. A separable two-part probe for detecting subsurface vibrations comprising: a first section including an antenna for transmitting radio frequency signals; a plurality of brake members attached to the exterior of the first section, said brake members each having a surface medium engagement portion for engaging the surface medium to bring the brake members into engagement with the surface medium for braking said first section to a stop such that said first section remains partially above said surface; a transducer section separably mating with said antenna section and including means for converting subsurface vibrations into radio frequency signals, means for electrically connecting the converting means of the transducer section to the antenna of said first section to transmit radio frequency signals representative of the subsurface vibrations; and releasable coupling means joining said first section to said transducer section to form a single unit operatively responsive to the brake action to release said sections upon engagement of said brake members with said surface medium thereby permitting said transducer section to be buried below the surface.
 10. A separable two-part probe for detecting subsurface vibrations as set forth in claim 9 wherein each of said brake members include terra spikes and said releasable coupling means includes retaining pins as part of the transducer section engaging detents formed in the terra spikes of the brake members attached to said first section.
 11. A separable two-part probe for detecting subsurface vibrations as set forth in claim 10 wherein said releasable coupling means further includes a force ring slidably mounted on the exterior surface of the transducer section and engaging the terra spikes to disengage the retaining pins from the detents upon contact of said force ring with a surface area.
 12. A separable two-part probe for detecting subsurface vibrations as set forth in claim 11 including an inflatable float attached to said force ring to force said force ring into engagement with the terra spikes to separate said section and to float said first section partially above the surface when dropped in a body of water.
 13. A separable two-part aerial drop probe for detecting subsurface vibrations comprising: a first cylindrical housing having stabilizing fins for stabilizing the glide path of said probe and including an antenna for transmitting radio frequency signals, a plurality of terra spikes attached to said first cylindrical housing and bendable into a braking position upon contact with a surface area to brake said housing to a stop such that it remains partially above the surface area, a second cylindrical housing having a cone-shaped end and separably mating with said first cylindrical housing and including means for converting subsurface vibrations into radio frequency signals, means for electrically connecting the converting means of the second housing to the antenna of the first housing to transmit radio frequency signals representative of the subsurface vibrations, and releasable coupling means joining said first housing to said second housing to form a single unit aerial drop probe, said coupling actuated to release said sections upon contact of braking means with a surface area.
 14. A separable two-part aerial drop probe for detecting subsurface vibrations as set forth in claim 13 wherein said releasable coupling includes: retaining pins located around the outer surface of said second housing engaging detents formed in the terra spikes attached to the first housing, and a force ring slidably encircling the second housing and engaging the terra spikes to disengage the retaining pins from the detents upon contact of said ring with a surface area.
 15. A separable two-part probe for detecting subsurface vibrations comprising: a first section including an antenna for transmitting radio frequency signals, a brake means, said brake means including a plurality of terra spikes attached to said first section, a transducer section separably mating with said antenna section and including means for converting subsurface vibrations into radio frequency signals, means for electrically connecting the converting means of the transducer section to the antenna of said first section to transmit radio frequency signals representative of the subsurface vibrations, and releasable coupling means joining said first section to said transducer section to form a single unit, said coupling means adapted to release said section upon contact of said brake means with a surface area.
 16. A separable two-part probe for detecting subsurface vibrations as set forth in claim 15 wherein said releasable coupling means includes: retaining pins as parT of a friction ring encircling the transducer section engaging detents formed in said terra spikes attached to the first section, a force ring slidably attached to the transducer section and engaging the terra spikes to disengage the retaining pins from the detents, and an inflatable float storable in said force ring for producing a force to activate said force ring when in an inflated condition. 